The initiation, rate of progress of periodontal disease and consequent tooth loss and associated microbiologic and immunologic factors are being investigated in a population never exposed to any programs or incidents relative to prevention and treatment of dental disease. Initially 480 male laborers at two tea plantations in Sri Lanka comprised the study group. The study design and baseline findings were reported in 1978. At the initial examination in 1970 the age of the participants ranged between 14 and 31 years. Subsequent examinations occurred in 1971, 1973, 1977, 1982 and 1985. Presently, the longitudinal study covers the age range 14-46 years. During the sixth survey in 1985 there were 161 individuals who had participated in the first survey. The time span between the first and sixth examination was 15 years. A cross-sectional sample was selected from a third plantation in January 1985, and consisted of 169 male tea laborers between 25 and 71 years of age. Three subpopulations have been identified based on interproximal loss of attachment and tooth mortality in both the longitudinal and cross-sectional groups: (1) individuals (8%) with rapid progression of periodontal disease (RP), those (81%) with moderate progression (MP), and a group (11%) who exhibited no progression of periodontal disease beyond gingivitis. The annual rate of destruction in the rapidly progressing (RP) group varied between 0.1 and 1.0 mm., in the moderately progressing (MP) group between 0.05 and 0.5 mm., and in the non-progressing disease groups (NP) between 0.05 and 0.09 mm.